1. Field of the Invention
This invention relates to the field of semiconductor processing and more specifically to a method for improving metal to interlayer dielectric (ILD) adhesion.
2. Background Information
The semiconductor industry is always pushing and striving to develop faster and faster semiconductor devices. One way that has been determined to increase the speed of semiconductor devices is to fabricate those devices with dielectric materials having low dielectric constants, i.e. low-k dielectric materials. The use of low-k dielectric materials have lead to a host of new problems that now must be dealt with in order to produce reliable devices.
One such problem is metal delamination from the low-k dielectric underlayer. As illustrated in FIG. 1, delamination occurs when the metal layer 120 and interlayer dielectric (ILD) 110 begin to xe2x80x9cpull awayxe2x80x9d from one another creating a gap 190. Metal delamination could potentially cause reliability problems and even cause device failure. Metal delamination tends to occur frequently when the metal-to-dielectric interface are subjected to high temperatures, for example temperatures of approximately 400xc2x0 C. or greater. Temperatures greater than 400xc2x0 C. are often reached during the various fabrication processes of a semiconductor device and thus could cause delamination between the metal layer and dielectric layers.
Other potential causes for delamination are contamination on the ILD surface and diffusion of dopants from the ILD. Contamination on the ILD surface degrades the metal to ILD adhesion because the contaminants block the metal from actually contacting the ILD surface in the areas that the contamination exists. If an ILD is a doped ILD, the dopants may diffuse from the ILD into the metal layer. The diffusion of the dopants tends to break down the adhesion between the metal and ILD at the metal to ILD interface.
One method to aid in the prevention of delamination is the use of an adhesion layer between the dielectric layer and the metal layer. FIG. 2a illustrates a dielectric layer 210 having an adhesion layer 230 deposited thereon. After the adhesion layer 230 is deposited on metal layer 220 is then deposited above the adhesion layer 230, as illustrated in FIG. 2b. 
One problem with adhesion layers is that they add processing steps to the manufacturing process. Any time processing steps and materials are added to a manufacturing process the cost, the time to complete the process, the potential for contamination, and the potential for errors all increase. Additionally, different metal and/or dielectric materials would require different adhesion materials. In other words, depending upon the type of metal layer to be formed above the dielectric layer different adhesion layers would probably have to be used. For example, the adhesion layer used for a tungsten metal layer would likely be different from the adhesion layer used for a copper metal layer or an aluminum metal layer.
Another method to aid in the prevention of delamination is the treatment of the dielectric layer with an argon plasma prior to the deposition of the metal layer. The argon plasma is used to remove the contaminants from the dielectric surface. The presence of contaminants on the dielectric surface tends to degrade the adhesion between the metal layer and the dielectric layer.
FIG. 3a illustrates a dielectric layer 310 being treated with an argon plasma 350. The argon plasma removes contaminants from the dielectric surface 310. Metal layer 320 is then deposited above dielectric layer 310, as is illustrated in FIG. 3b. Although contamination is reduced between the metal layer 320 and dielectric layer 310, the use of the argon plasma 350 does not help to prevent delamination caused by the diffusion of dopants from the dielectric layer 310. The diffusion of dopants from dielectric layer 310 degrades the adhesion at the metal layer 320 and dielectric layer 310 interface. Thus, delamination may still occur and metal layer 320 may lift from the underlying dielectric layer 310 forming gap 390, as is illustrated in FIG. 3c. 
What is needed is a method to improve the dielectric to metal adhesion such that delamination will not occur and gaps are not formed.
The present invention is a method to improve metal to dielectric adhesion. A dielectric layer is deposited, then a surface of the dielectric layer is modified to improve adhesion from the dielectric layer. A metal layer is then deposited above the modified surface of the dielectric layer.
Additional features and benefits of the present invention will become apparent from the detailed description, figures, and claims set forth below.